Biological tissue/bone healing and growth have recently attracted a great deal of research interest in various medical fields. For example, after traumatic luxation and avulsion injury to teeth, root resorption becomes a major concern [1, 2, 3]. A favorable crown to root ratio is important to support a tooth and to withstand occlusal forces. Increased root resorption is commonly observed during orthodontic tooth movement in humans [4].
In severe resorption, where the teeth crown to root ratio is adversely affected, increased teeth mobility is often observed in patients and splinting of these teeth may be required in some patients [5]. Another adverse outcome of teeth root resorption is the increased liability facing orthodontists from malpractice claims [6]. The healing pattern generally depends on the degree and surface area of the damaged root and on the nature of an inflammatory stimulus [2, 7]. If the root damage is small, it can be healed by new cementum. However, if the root damage is large, bone may attach directly onto the root surface resulting in ankylosis; thereafter osseous replacement and healing by new cementum is questionable [8, 9]. Infection can cause progressive inflammatory resorption that can in turn cause tooth loss in a very short period of time.
It has been reported that 66% of tooth loss following trauma is due to root resorption and half of these cases involve a progressive type of root resorption [10]. Non-invasive methods for tissue healing include electric stimulation [11], pulsed electromagnetic field (PEMF) [12], and low intensity pulsed ultrasound (LIPUS) [13]. In animal studies involving rabbits, a LIPUS device has been used for bone healing and formation during mandibular distraction osteogenesis [13]. LIPUS has also been used to stimulate dental tissue formation and enhance teeth eruption [14]. In human studies, a LIPUS device has been used for the healing of orthodontically-induced teeth root resorption [15] and this was supported by other in-vitro studies [23].
Studies show that with suitable pulse durations and power densities, LIPUS pulses are very effective for enhancing dental-tissue healing and for treating the tooth-shortening problem. A congenital anomaly known as Hemifacial microsomia, characterized by an underdeveloped mandible (lower jaw) on one side, has also been treated using a LIPUS device to stimulate bone growth in the deficient side, giving patients a more symmetric jawline [16].
Although success in using therapeutic ultrasound has been repeatedly demonstrated, devices that are traditionally used for applying ultrasound to a treatment area are bulky, and require a patient to hold the device in place during treatment. Control of the intensity of ultrasound applied by these devices also tends to be difficult. For example, currently available devices use wired communications, and the possibility of saliva contacting a wire may cause short circuits and endanger a patient.